2019AJ....158...34D

We report the very bright detection of cold molecular gas with the IRAM NOEMA interferometer of the strongly lensed source WISE J132934.18+224327.3 at z = 2.04, the so-called Cosmic Eyebrow. This source has a similar spectral energy distribution from optical-mid/IR to submillimeter/radio but significantly higher fluxes than the well-known lensed SMG SMMJ 2135, the Cosmic Eyelash at z = 2.3. The interferometric observations unambiguously identify the location of the molecular line emission in two components, component CO32-A with I_CO(3–2)=52.2±0.9 Jy km s^–1 and component CO32-B with I_CO(3–2)=15.7±0.7 Jy km s^–1. Thus, our NOEMA observations of the CO(3-2) transition confirm the SMG-nature of WISE J132934.18+224327.3, resulting in the brightest CO(3-2) detection ever of an SMG. In addition, we present follow-up observations of the brighter component with the Green Bank Telescope (CO(1-0) transition) and IRAM 30 m telescope (CO(4-3) and [C I](1-0) transitions). The star formation efficiency of ∼100 L_☉/(K km s^–1 pc²) is at the overlap region between merger-triggered and disk-like star formation activity and the lowest seen for lensed dusty star-forming galaxies. The determined gas depletion time ∼60 Myr, intrinsic infrared star formation SFR_IR ≃ 2000 M_☉ yr^–1, and gas fraction M_mol/M_* = 0.44 indicate a starburst/merger-triggered star formation. The obtained data of the cold ISM-from CO(1-0) and dust continuum-indicates a gas mass µM_mol ∼ 15 x 10¹¹ M_☉ for component CO32-A. Its unseen brightness offers us the opportunity to establish the Cosmic Eyebrow as a new reference source at z = 2 for galaxy evolution.